|Year : 2015 | Volume
| Issue : 4 | Page : 559-562
Thyroid hemiagenesis with isthmic agenesis: A case report with review of the literature
Sanjay M Khaladkar, Sahil Garg, Preeti Sherawat, Anubhav Kamal
Department of Radiodiagnosis, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth, Pune, India
|Date of Web Publication||14-Jul-2015|
Sanjay M Khaladkar
Flat No. 5, Plot No. 8, Tejas Building, Sahawas Society, Karve Nagar, Pune - 411 052, Maharashtra
Source of Support: None, Conflict of Interest: None
Thyroid hemiagenesis (THG) is a rare congenital anomaly in which one lobe of thyroid gland fails to develop. Agenesis may be unilateral, total or isthmic. Left thyroid lobe is commonly involved than right lobe in hemiagenesis. Clinically patients can be euthyroid, hypothyroid or hyperthyroid. Often it is diagnosed as an incidental finding during ultrasonography (USG) study of neck, which easily diagnose this condition. Actual incidence of THG is unknown, most cases are diagnosed in patients admitted for thyroid scan or thyroid surgery because of suspicion of other thyroid abnormalities. This explains high frequency of association of hemiagenesis with other thyroid abnormalities such as multinodular goiter, adenoma, hyperthyroidism, hypothyroidism, chronic thyroiditis, and carcinoma. We report a case of 58-year-old male patient detected to have hemiagenesis of left thyroid lobe and isthmus when USG neck was performed for carcinoma right buccal mucosa with metastatic cervical lymphadenopathy.
Keywords: Congenital thyroid anomalies, hemiagenesis, thyroid
|How to cite this article:|
Khaladkar SM, Garg S, Sherawat P, Kamal A. Thyroid hemiagenesis with isthmic agenesis: A case report with review of the literature. Med J DY Patil Univ 2015;8:559-62
|How to cite this URL:|
Khaladkar SM, Garg S, Sherawat P, Kamal A. Thyroid hemiagenesis with isthmic agenesis: A case report with review of the literature. Med J DY Patil Univ [serial online] 2015 [cited 2020 Oct 21];8:559-62. Available from: https://www.mjdrdypu.org/text.asp?2015/8/4/559/160815
| Introduction|| |
Congenital thyroid anomalies are rare. They are related to abnormal descent of thyroid gland or to structural abnormalities in thyroid development such as hypoplasia or agenesis with or without isthmic agenesis. They are usually due to abnormal descent rather than abnormal development. 
Thyroid is the first endocrine gland to start developing in the embryo.  Thyroid developmental anomalies (excluding biochemical abnormalities) are divided into 3 groups - agenesis (or arthyreosis), dysgenesis and anomalies due to the persistence of a thyroglossal duct. Thyroid dysgenesis (TD) include thyroid hemiagenesis (THG), Thyroid hypoplasia, ectopic, aberrant and accessory thyroid tissue. THG anomaly was first described in 1852 by Handsfield Jones.  Hypoplasia or agenesis of one or both lobes with or without agenesis of isthmus is a rare developmental anomaly. Hemiagenesis of either lobe with or without isthmic agenesis is a very rare developmental anomaly with a prevalence rate of around 0.2% in asymptomatic children.  Left side is most commonly involved in hemiagenesis (80%). Isthmus may be absent in 40-50% cases. 
| Case Report|| |
A known case of squamous cell carcinoma of right buccal mucosa (proved on biopsy) with lymphadenopathy on the right side of the neck was referred for ultrasonography (USG). USG neck showed a fairly well-defined hypoechoic lesion measuring approximately 2.5 cm × 0.9 cm × 1.1 cm in right buccal mucosa suggestive of neoplastic etiology. Multiple lymph nodes of size 1-2 cm were noted in right submandibular region (level 1B) showing few small central anechoic necrotic areas-likely to be metastatic lymph nodes. Both parotid and submandibular salivary glands appear normal. Neck vessels on either side appear normal. No other cervical lymphadenopathy noted on either side of the neck.
Right thyroid lobe measured approximately 4.2 cm (Length) × 1.8 cm (Antero-posterior) × 1.6 cm (Transverse). Isthmus and left thyroid lobe were not seen [Figure 1] [Figure 2] [Figure 3]. There was no previous history of any thyroid surgery. Hence, the diagnosis of agenesis of left thyroid lobe and isthmus was made on USG. Computed tomography (CT) neck was performed for staging of carcinoma buccal mucosa and showed normal right thyroid lobe and absence of isthmus and left thyroid lobe confirm diagnosis of hemiagenesis of left thyroid lobe with isthmus [Figure 4].
|Figure 1: Ultrasonography transverse section of lower neck showing normal right thyroid lobe, absent left thyroid lobe|
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|Figure 2: Ultrasonography longitudinal section of lower neck showing normal right thyroid lobe, absent left thyroid lobe|
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|Figure 3: Ultrasonography transverse section of lower neck showing normal right thyroid lobe, absent left thyroid lobe and isthmus|
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|Figure 4: Postcontrast computed tomography scan transverse section of lower neck showing normal right thyroid lobe, absent left thyroid lobe and isthmus|
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Thyroid function tests revealed-T3-110 ng/dl (normal range: 75-200 ng/dl), T4 - 6.2 ug/dl (4.5-11.5 ug/dl), TSH-0.8 u/ml (0.3-5 u/ml) suggestive of euthyroid state.
The aim of this case report is to increase awareness of this rare anomaly of thyroid gland and help to make preoperative diagnosis possible. Preoperative recognition of THG in patients undergoing thyroidectomy is useful in avoiding unnecessary exploration of one side of the neck thus reducing morbidity.
| Discussion|| |
Thyroid hemiagenesis is a rare congenital anomaly in which one lobe of thyroid gland fails to develop. Agenesis may be unilateral, total or isthmic.  Left sided hemiagenesis is more common than right sided hemiagenesis with a Left to right ratio of 4:1.  It is common in females with female to male ratio of 3:1.  Right sided hemiagenesis is a very rarely encountered. 
Thyroid gland develops as a median thickening of endoderm on floor of pharynx between first and second pharyngeal pouches. Later, this area invaginates to form a median diverticulum which appears in the later half of 4 th week. The median diverticulum grows as a bifurcating tubular duct from which both isthmus and both lateral lobes of the thyroid are developed.  Though the cause of unilateral agenesis of thyroid gland is not known, it is believed to arise from the failure of original anlage to become bilobed and spread out laterally to both sides. 
Though the cause of this anomaly is unknown there are two proposed theories related with etiology are a descent defect from floor of primitive pharynx to trachea, failure of original anlage to become bilobed and spread out laterally to both sides. 
Review of literature in year 2000 documented 256 cases of hemiagenesis. 51 New cases were published between 2000 and 2007 in English literature.  Left sided hemiagenesis is more common than right sided hemiageness with a Left to right ratio of 4:1.  In 2845, Belgian school children screened by USG for congenital thyroid anomalies, the prevalence of THG was 0.2%.  310 cases of THG have been reported in world literature to date. 
Most cases of THG are diagnosed when patients present with a lesion in functioning lobe. Clinically hemiagenesis of thyroid lobe and isthmic agenesis can be suspected if tracheal rings are easily palpated and edge of sternomastoid on the affected side is nearer the midline overlying the trachea. 
Actual incidence of THG is unknown, most cases are diagnosed in patients admitted for thyroid scan or thyroid surgery because of suspicion of other thyroid abnormalities. This explains high frequency of association of hemiagenesis with other thyroid abnormalities like multinodular goiter, adenoma, hyperthyroidism or hypothyroidism, chronic thyroditis and carcinoma. 
Thyroid hemiagenesis was first described in 1895 by Marshall. He found one case in 60 autopsies of children.  Discovery rate of THG by scanning was reported by Andrew to be 7 cases in 708 scans and Hamburger and Hamburger to be 4 in 7000 patients. A large study conducted in 1972 on 12456 patients undergoing surgery revealed 7 cases of THG. Friedman et al. in 1979 found 6 cases of THG in 12000 scans.  Melnick and Stenkowski reported 4 patients with THG and described hockey stick sign by imaging studies in case of THG. They reviewed the literature that revealed a total 94 cases of THG in 1981. Till 1986, 13 more reported cases of THG were reported. Thus bringing the total to just over 100.Between 1986 and 1999, most of the studies were designed as case reports.  Bandao et al. described a case of THG with Grave's hyperthyroidism developed from hypothyroidism and revealed a total of 196 cases of THG from literature in 1999.  In 2003, a THG with multinodular goiter was reported from Turkey and their review of literature revealed 270 cases with THG. After this study 5 more case reports with THG are reported in literature thus bringing total to over 270. The absence of left lobe and right lobe is encountered in 80% and 20% respectively. Isthmus is absent in 50% cases.  Hemiagenesis of left thyroid lobe at surgery was reported from India by Das in 1962.  In literature, most patients detected to have THG had accompanying thyroid disorders because absence of one thyroid lobe is usually asymptomatic. True prevalence of THG is not known, but estimated 0.02% in normal children. Prevalence of THG ranged between 0.05% and 0.2% in most of the studies and is more prevalent in females with absence of left thyroid lobe.  Gursoy et al. found that prevalence of hemiagenesis of thyroid lobe was 0.25% of patients presenting with various thyroid disorders whereas its prevalence in normal population was only 0.025%.  Many workers claim that absence of isthmus is quite rare in humans. Study conducted by Braun et al. found that isthmus was missing in 4 cases of 58 cadavers studied.  Won and Chung reported in 3% of cases studied isthmus was absent and lateral lobes of thyroid were separated.  Pastor et al. stated that isthmic absence can be associated with other types of dysorganogenesis like absence of lobe or presence of ectopic thyroid tissue.  In 1952, Allan reported absence of isthmus of thyroid gland. He stated that isthmus was absent in 2-4% cases. He observed a band of connective tissue (levator glandulae thyroidae) extending from apex of right or left thyroid lobe or isthmus of thyroid gland to hyoid bone. 
Four genes involved in thyroid gland development have been identified. Three encode thyroid specific transcription factors (TTF-1 or Nkx2, TTF-2 or FOXE1 a d Pax8) and one encodes TSH receptor gene. Pax8 gene may be a candidate gene for THG.  THG may be a familial disease. THG can occur as a familial disease with any form of TD. Mutations in these genetic factors are believed to be responsible for TD aqnd congenital hypothyroidism. In addition, environmental factors and genetic predospition are also proposed. 
Thyroid hemiagenesis was first described by Handsfield John in 1866.  The functioning lobe of thyroid gland can be a site of pathological changes similar to normally developed gland and may present with a spectrum of diseases like multinodular goiter, colloid goiter, follicular adenoma, thyroiditis, hypothyroidism and hyperthyroidism. Other associated anomalies with THG include unilateral absence of superior and inferior thyroid artery and right sided aortic arch. Thyroid agenesis should be suspected clinically when there is no palpable thyroid tissue felt on one or either side of the neck. Radiological investigations hold a key role in detecting THG. USG, CT and thyroid scintigraphy are useful in detecting this condition. USG is cheaper, easily available, easy to perform with no radiation hazards. Thyroid scintigraphy is useful in THG from a suppressed lobe. It will show total absence of uptake while THG activity will reappear in suppressed lobe.  Thyroidal hemiagenesis with presence of isthmus has the appearance of a hockey stick on 99 m technetium pertechnetate thyroid scan. 
This article emphasizes that surgeons are planning a thyroidectomy should be aware of rare anatomical variations so that these anomalies are not overlooked in the differential diagnosis, investigations and treatment.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]